#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	int n = 0;
	int sum = 0;
	scanf("%d", &n);
	long a = 0;
	for(sum=0;sum<=n;sum++)
	{
		a +=sum;	
	}
	printf("%d", a);
	return 0;
}

